fix: migration: set premigration to 90 minutes

[rjan90]

As discussed on slack. Current estimated premigration time for nv21 is 20 minutes - and setting the premigration to 90 minutes before the upgrade epoch should give ample of time for the migration to finish.

Proposed Changes

Move premigration to 90 minutes before the upgrade epoch.

Additional Info

• Needs backport to release/v1.24.0 before cutting final release
• Needs backport to release/v1.25.0 before cutting final release

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, build, chore, ci, docs, perf, refactor, revert, style, test
  • area, e.g. api, chain, state, market, mempool, multisig, networking, paych, proving, sealing, wallet, deps
• If the PR affects users (e.g., new feature, bug fix, system requirements change), update the CHANGELOG.md and add details to the UNRELEASED section.
• New features have usage guidelines and / or documentation updates in
  • Lotus Documentation
  • Discussion Tutorials
• Tests exist for new functionality or change in behavior
• CI is green